The invention relates to a circuit breaker comprising means for measuring the current flowing in conductors to be protected and designed to cooperate with a standard removable electronic trip device comprising a processing circuit producing a tripping signal when the measured current exceeds preset tripping thresholds.
Circuit breakers can generally be used with different types of electronic trip devices, which are therefore generally removable and are only fitted in a circuit breaker when the latter is installed. Conventional electronic trip devices perform the long delay and/or short delay and/or instantaneous tripping functions, and possibly an earth protection function. For these different functions, the tripping threshold settings can generally be adjusted by the user. It is also preferable for the trip device to perform an instantaneous tripping function designed to protect the circuit breaker, whose threshold is adjusted to suit the circuit breaker type and rating so as to be adapted to the electrodynamic withstand of the circuit breaker. This instantaneous tripping function is conventionally achieved by means of an analog trip circuit of the trip device whose threshold is set in the manufacturing plant on the trip device, according to the circuit breaker for which it is intended. In present-day circuit breakers the current transformers, fixedly secured to the circuit-breaker, are designed in such a way as to supply a predetermined current, typically 100 mA, on the secondary winding when a rated current of preset value, for example 160A, 250 A, 400A or 630A, flows through their primary winding. The trip device processing circuit processes the signals which are supplied to it by the current transformers without taking account of the rated current value, the tripping thresholds being defined in relative value with respect to this rated current, at least in the case of the long delay, short delay and instantaneous tripping functions. In some cases, however, the processing circuit has to know the rated current value, notably when the trip device comprises means for displaying the current flowing in the conductors to be protected, for communication with a remote monitoring device and, sometimes, for earth protection. Up to now this information has been supplied to the trip device in the plant, according to the circuit breaker for which it is intended. In the case of microprocessor-based trip devices, this is conventionally achieved by means of an individualization box which supplies, in the plant, the rated current value to a memory of the microprocessor.
The type and/or rating of the circuit breaker in which the trip device is to be fitted therefore has to be known in advance when a trip device is manufactured.